Redundant current driver



Dec. 3, 1968 J. D. HAGEE REDUNDANT CURRENT DRIVER Filed Nov. 26, 1965 POWER SUPPLY 5 MAGNETIC CORE uun iNHIBIT CIRCUIT DRIVER UNIT nY H M H U M 1 a i /1 I k L w m .r 1. |||l .IIIIVL 0 6 x 4 I H A 2 6 m n M lllilL "lJilI J I ,0 m M f i L M. w MN MW 2 MV Z 5 M) w m Q 14 LOAD -l INVENTOR- JOHN D.HAGEE BY ATTORNEY United States Patent 3,414,736 REDUNDANT CURRENT DRIVER John D. Hagee, Havertown, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed Nov. 26, 1963, Ser. No. 325,958 11 Claims. (Cl. 307-219) This invention relates to current drivers and more particularly to a current driver which is capable of maintaining a constant load current and which has a greater reliability than some of its circuit components.

It is frequently desirable to generate electrical current pulses for rapidly activating other electrical networks. The circuits which are utilized to generate these electrical current pulses are sometimes called current drivers. Current drivers, for example, may be used to switch a magnetic core memory from one state to another.

In switching magnetic cores the current driver must provide a constant current through the load independent of load variations or power supply variations. The current driver should also have a high reliability. It should continue to operate even though some of its components fail. Accordingly, it is an object of this invention to provide an improved current driver.

It is a further object of this invention to provide a current driver in which the load current is relatively independent of load variations and power supply variations.

It is a further object of this invention to provide a transistorized current driver which will operate after a failure of any transistor or circuit component.

In accordance with the above objects, a current driver is provided which includes two units each independently capable of providing the required amount of current. The

current within the units is regulated by a transformer. Redundant components are used in each of the units so that they will continue to operate even though a component is shorted out. When one unit is operating, the other is inhibited through one of its regulating transformers.

The invention and the above-noted and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawings in which:

FIGURE 1 is a block diagram of an embodiment of the invention;

FIGURE 2 is a schematic circuit diagram of one portion of the embodiment of the invention shown in FIG- URE 1; and

FIGURE 3 is a schematic circuit diagram of the embodiment of the invention shown in FIGURE 1.

In FIGURE 1 the block diagram of a current driver that illustrates an embodiment of the invention is shown having an input terminal electrically connected to both a driver unit 12 and to a driver unit 14. The driver unit 12 is electrically connected to the magnetic core unit 16, which is the load, through the inhibit circuit 18. The inhibit circuit 18 is electrically connected to the driver unit 14; and the driver unit 14 is connected to the mag netic core unit 16. The magnetic core unit 16 is also connected to a power supply 20.

The power supply 20 has its positive output terminal electrically connected to the magnetic core unit 16 so as to draw electrons from the driver through the magnetic core unit whenever the driver is activated by a positive input voltage pulse on terminal 10. A positive input voltage pulse on terminal 10 activates the driver unit 12 so as to provide a path for current, from the power supply 20, through the magnetic core unit 16, through the inhibit circuit 18, and to ground in the driver unit 12. The current flow through the inhibit circuit 18 activates this circuit so that it holds the driver unit 14 open (nonconducting). However, if a fault occurs in the driver unit 12 while a positive input pulse is applied to terminal 10, the inhibit circuit 18 is deactivated and the: driver unit 14 is grounded. In this case electrons flow from the driver unit 14 through the magnetic core unit 16 to the power supply 28. Thus an alternate path is provided for current in the case of a fault.

In FIGURE 2 a schematic circuit diagram of the driver unit 12 is shown having an input terminal 22, a first transformer 24, a second transformer 26, and a third transformer 28. The input terminal 22 is electrically connected in series with a 1K (kiloohm) resistor 30, a 1N482A diode 32 and the terminal 34 in the order named with the cathode of the diode 32 directly connected to the terminal 34. The terminal 34 is connected to ground through the parallel combination of a 12 volt Zener diode 36, a 12 volt Zener diode 38 and an turn winding 40 of the 7F160-3C pulse transformer 28, with the cathodes of both Zener diodes directly connected to the terminal 34.

The terminal 34 is also electrically connected to one end of a turn winding 42 of the 7F1603C pulse transformer 24 and to one end of the 68 ohm resistor 44; the other end of the transformer winding 42 and the other end of the resistor 44 are electrically connected together and to the anode of the 1N982A diode 46. The cathode of diode 46 is electrically connected to the base of the 2N718A transistor 48 and to one end of the 33K resistor 50. The transistor 48 is of the NPN type. The other end of the resistor 50 and the emitter of the transistor 48 are each grounded.

The collector of the transistor 48- is electrically connected to the emitter of the 2N718A transistor 52, to one end of the 33K resistor 54, and to one end of the 80 turn winding 56 of the pulse transformer 28. The transistor 52 is of the NPN type. The winding 56 is wound in the same direction as the winding 40. The other end of the resistor 54 is electrically connected to the cathode of the 1N482A diode 58 and to the base of transistor 52. The other end of the winding 56 is electrically connected to the terminal 60. The anode of the diode 58 is electrically connected to the terminal 60 through the parallel combination of a 160 turn winding 62 of the 7F160-3C pulse transformer 26 and a 68 ohm resistor 64.

The collector of the transistor 52 is electrically connected in series with a 40 turn winding 66 of the trans former 24, a 20 turn winding 68 of the transformer 26, a 20 turn winding 70 of the transformer 28, a load 72 and a source of positive voltage 74 in the order named. The winding 66 is wound in the same direction as the winding 42; the winding 68 is wound in the same direction as the winding 62; and, the winding 70 is wound in the opposite direction as the winding 56.

A positive input pulse on terminal 22 drives current through the winding 40 of the transformer 28 and also biases the transistor 48 to conduction. The current through the winding 40 develops a voltage in the winding 56 which biases the transistor 52 into conduction. The two Zener diodes 36 and 38 shunting the winding 40 to regulate the voltage from the input terminal 22. Two Zener diodes are used for safety in case one should fail.

When both the transistors 48 and 52 are biased into conduction, a path is provided from the positive voltage source 74 through the load 72, the transformers 28, 26, 24, and the transistors 52 and 48 for current to flow to ground.

The current through the winding 70 induces a regenerative voltage in windings 40 and 56 and this voltage is clamped to a predetermined level by reference diodes 36 and 38. The current through winding 68 .induces a voltage in winding 62 which is opposite in polarity to that induced in winding 56. The net voltage appearing between base and emitter of transistor 52 is the algebraic sum of these voltages. The current through winding 66 induces a voltage in winding 42 which is opposite in polarity to that induced in winding 40. Again, the net voltage appearing between base and emitter of transistor 48 is the algebraic sum of these voltages. The voltages appearing across windings 42 and 62 is a function of the current in the load and will maintain a constant load or collector current over wide ranges in transistor gain, power supply variations and load impedance variations. If one of the transistors is shorted, regulation will be maintained by the constant current characteristics of the other transistor and associated circuitry.

In FIGURE 3 a schematic circuit diagram of the current driver is shown with the necessary connections between the driver unit 12 and the driver unit 14, which has the same structure as the driver unit 12 and with the inhibit circuit 18.

The input terminal 22 is electrically connected to ground through a resistor 76, a diode 78, terminal 80, and the parallel combination of a Zener diode 82, a Zener diode 84, and a transformer winding 86, all in series in the order named. The components have the same connections and the same values as those in the driver unit 12. However, a 480 ohm resistor 88 and a 480 ohm resistor 90 are each electrically connected in parallel across the transformer winding 86.

Furthermore, the terminal 80 is electrically connected to the base of the NPN transistor 92 through the parallel combination of the resistor 94 and the transformer winding 96 in series with a diode 98, to the emitter of the transistor 92 through resistor 100, and to ground through the same resistor 108, in the same type of connection and with the same type and value of components as the terminal 34 in the driver unit 12 of FIGURE 2. A transistor 102 has its emitter electrically connected to the collector of transistor 92 and has its collector electrically connected to a source of positive voltage 74 through the transformer winding 104, the transformer winding 106, the transformer winding 108, and the load 72, in series in the order named, and has its emitter electrically connected to its base directly through a resistor 112 and also through the series combination of a transformer winding 114, the transformer winding 116 shunted by resistor 118, and a diode 120 just as was described in connection with the driver unit 12. However, the transformer having windings 86, 114 and 108 also has a fourth winding 122 wound in the same direction as winding 86. This winding is electrically connected at one end to the output of the driver 12 and at the other end to both the load 72 and to the output of the driver 14.

A positive input pulse on terminal 22 causes current to be drawn from the positive voltage source 74 through the load 72 through the transistors 52 and 48 to ground in the manner described in connection with FIGURE 2. The driver unit 12 draws current before the driver 14 because of the two resistors 88 and 90. These two resistors reduce the resistance from the input terminal 22 to ground causing the voltage drop across the resistor 76 to be greater than the voltage drop across the resistor 30. This means that the current in the winding 86 will not build up as quickly or, more significantly, decrease as quickly at the end of the input pulse as the current in the winding 40 and, therefore, assures that driver 12 will commence conduction first and clamps reverse polarity voltage induced in Winding 86 at the end of the input pulse which prevents driver 14 from producing an output pulse at that time. Current drawn through the driver unit 12 flows through the winding 122. This current in the winding 122 reduces the voltage in the winding 108 of the same transformer and in the winding 86 and winding 114 which tend to hold the transistors 92 and 102 in their non-conducting state. As long as driver unit 12 draws the required amount of current through the load 72 the driver unit 14 will be held off. However, if an open occurs in the driver unit 12 so that it stops drawing current through the load 72, the

inhibiting voltage from the transformer winding 122 is removed and the driver unit 14 is free to conduct current on receipt of an input pulse from terminal 22.

Of course, an emitter follower type current driver may be used in driver units 12 and 14. This would require the use of a total of two transformers, but would increase the voltage drop in the collector circuit. This approach would be desirable if the magnitude of the power supply voltage was not restricted.

It can be seen that the circuit shown in FIGURE 3 provides reliable operation. The current through the load is maintained constant in spite of the load variations, transistor parameter variations, and power supply variations. It continues to operate even after there is an open or short in one of its components.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A current driver comprising:

an input terminal adapted to receive trigger voltages;

a bias terminal and an output terminal adapted to provide electrical energy to a load; first current-valve means, having a first electrode electrically connected to said input terminal, a second electrode and a third electrode connected to the bias terminal, for reducing the resistance between said second and third electrodes upon receiving a voltage on said first electrode from said input terminal;

second current-valve means, having a first electrode electrically coupled to said input terminal, having a second electrode electrically connected to said output terminal and having a third electrode electrically connected to said second electrode of said first current valve means, for reducing the resistance between said second electrode and said third electrode upon receiving a voltage from said input terminal on said first electrode; coupling means, coupling said first electrode of said first current-valve means to said second electrode of said second current-valve means and coupling said first electrode of said second current-valve means to said second electrode of said second current-valve means, for generating voltages on said first electrodes of said first and second current-valve means whenever current in said current valve means exceeds a predetermined magnitude; said coupling means being characterized by having at least one transformer winding electrically connected to said second electrode of said second currentvalve means, at least one transformer winding electically connected to said first electrode of said first current-valve means, and having at least one transformer winding electrically connected to said first electrode of said second current-valve means. 2. A current driver according to claim 2 in which said coupling means further comprises an inhibit means connected to a current source terminal for preventing current flow through the coupling means between said second electrode of said second current-valve and said output terminal whenever said load is receiving current through the inhibit means.

3. A current driver according to claim 3 in which said inhibit means comprises a transformer winding electrically connected to said current source terminal and to said load.

4. The combination comprising: first means responsive to an electrical waveform for causing electric current to flow through a load;

second means, electrically connected in parallel with said first means and responsive to said electrical waveform, for causing electric current to flow through said load; and

transformer coupling means, electrically connected between said first means and said load and coupled to said second means and responsive solely to conduction in said first means for disabling said second means whenever said first means is causing said electric current to flow through said load.

5. The combination comprising:

an input terminal adapted to receive circuit input pulses;

first current-valve means, having a first terminal electrically connected to said input terminal, having a second terminal and having a third terminal which is grounded, for reducing the resistance between said second terminal and said third terminal upon receiving a voltage pulse from said input terminal;

second current-valve means, having a first terminal which is electrically connected to said input terminal, having a second terminal and having a third terminal which is grounded, for reducing the resistance between said second terminal and said third terminal upon receiving a voltage pulse from said input terminal; and

coupling means, electrically connected to said second terminal of said first current-valve means and electrically coupled to said first terminal and to said second terminal of said second current-valve means, for preventing the flow of current through said second terminal of said second curent-valve means While current is flowing through said second terminal of said first curent-valve means.

6. The combination according to claim 6 in which said first current-valve means and said second currentvalve means each comprises a transistor having one electrode electrically connected to ground, a second electrode electrically connected to said input terminal and a third electrode electrically connected to the second terminal thereof.

7. The combination according to claim 6 in which said first current-valve means and said second currentvalve means each further comprises a transformer having one winding electrically connected between a third electrode of said transistor and said second terminal of said current-valve means and having another winding of said transformer electrically connected between said second electrode of said transistor and said input terminal.

8. The combination according to claim 7 in which said second current-valve means comprises one winding of a transformer electrically connected between said second electrode of said transistor and said input terminal and in which said coupling means comprises a second winding of the same transformer electrically connected between said second terminal of said first current-valve means and said second terminal of said second current-valve means.

9. A redundant current driver comprising:

an input terminal adapted to receive positive trigger voltages;

a first NPN transistor having its base electrically connected to said input terminal and having its emitter grounded;

a second NPN transistor having its base electrically coupled to said input terminal and having its emitter electrically connected to the collector of said first transistor;

a third NPN transistor having its base electrically connected to said input terminal and having its emitter grounded;

a fourth NPN transistor having its emitter electrically connected to the collector of said third NPN transistor and having its base electrically coupled to said input terminal;

an output terminal adapted to be connected to a load; and

a transformer having a first winding electrically connected between the collector of said second transistor and said output terminal and having a second winding wound in the opposite direction as said first winding and being electrically connected between the collector of said fourth transistor and said output terminal.

10. A current driver comprising:

first, second, third, fourth, fifth and sixth pulse transformers;

an input terminal adapted to receive trigger voltages;

a first resistor having its first end electrically connected to said input terminal;

a first winding of said first transformer having a first end electrically connected to the second end of said first resistor and having a second end grounded;

a first Zener diode having its cathode electrically connected to said first end of said first winding of said first transformer and having its anode electrically connected to said second end of said first winding of said first transformer;

a first NPN transistor having its emitter grounded;

a first winding of said third transformer having a first end electrically connected to the base of said first NPN transistor and having a second end electrically connected to the first end of said first winding of said first transformer;

a second NPN transistor having its emitter electrically connected to the collector of said first NPN transistor;

a first winding of said second transformer having a first end electrically connected to the base of said second transistor;

a second winding of said first transformer wound in the same direction as said first winding of said first transformer and having a first end electrically connected to said second end of said first winding of said second transformer and having; a second end electrically connected to the emitter of said second transistor;

a second winding of said third transform-er having a first end electrically connect-ed to the collector of said second transistor;

a second winding of said second transformer wound in the same direction as said first winding of said second transformer and having a first end electrically connected to the second end of said second winding of said third transformer;

a third winding of said first transformer wound in the opposite direction as said first winding of said first transformer and having a first end electrically connected to the second end of the second Winding of said second transformer;

an output terminal adapted to be connected to a load;

a first Winding of said fourth transformer having a first end electrically connected to the second end of the third winding of said first transformer and having a second end electrically connected to said output terminal;

a second resistor having a first end electrically connected to said input terminal;

a second winding of said fourth transformer having a first end electrically connected to the second end of said second resistor and having a second end grounded, and being wound in the same direction as said first winding of said fourth transformer;

a third resistor having a first end electrically connected to the second end of said second resistor and having a second end grounded;

a second Zener diode having its cathode electrically connected to the second end of said second resistor and having its anode grounded;

a third NPN transistor having its emitter grounded;

a first winding of said sixth transformer having a first end electrically connected to the base of said third transistor and having a second end electrically connected to the first end of said second winding of said fourth transformer;

a fourth NPN transistor having its emitter electrically connected to the collector of said third transistor; first winding of said fifth transformer having a first end electrically connected to the base of said fourth transistor;

third winding of said fourth transformer wound in the same direction as said second Winding of said fourth transformer and having a first end electrically connected to the second end of said first winding of said fifth transformer and having a second end electrically connected to the emitter of said fourth transistor;

second winding of said sixth transformer wound in the same direction as said first Winding of said sixth transformer and having a first end electrically connected to the collector of said fourth transistor; second winding of said fifth transformer wound in the same direction as said first winding of said fifth transformer and having a first end electrically connected to the second end of said second winding of said sixth pulse transformer; and

fourth winding of said fourth transfonrner having a first end electrically connected to said second end of said second winding of said fifth transformer and having a second end electrically connected to said output terminal and being wound in the opposite direction as said second winding of said fourth transformer.

11. Redundant constant current driver apparatus for a load comprising:

first current-valve means responsive to an electrical waveform for causing an electric current to flow in said load;

second current-valve means, electrically connected in parallel With said first current-valve means and responsive to said electrical waveform, for causing said electric current to flow in said load; and

inductive coupling means electrically connected in series with said first current-valve means and coupled to said second current-valve means and responsive to conduction in said first current-valve means for inhibiting said second curent-valve means whenever said first current valve means is causing said electric current to flow in said load.

References Cited JOHN S. HEYMAN, Primary Examiner. .T. ZAZWORSKY, Assistant Examiner. 

4. THE COMBINATION COMPRISING: FIRST MEANS RESPONSIVE TO AN ELECTRICAL WAVEFORM FOR CAUSING ELECTRIC CURRENT TO FLOW THROUGH A LOAD; SECOND MEANS, ELECTRICALLY CONNECTED IN PARALLEL WITH SAID FIRST MEANS AND RESPONSIVE TO SAID ELECTRICAL WAVEFORM, FOR CAUSING ELECTRIC CURRENT TO FLOW THROUGH SAID LOAD; AND 